Figure 2.

Two-dimensional density plot of novel genome 'specific genes' for the E. coli pan-genome. The plot illustrates the number of novel genome specific genes for the nth genome when comparing n = 2,...,32 genomes (for a maximum of 3,200 random combinations at each n). The density colors reflect the count of combinations giving rise to a certain number of specific genes (y-axis) in one genome compared to n - 1 other genomes; that is, for n = 2, genome number 2 is compared to genome number 1 and, on average, approximately 650 genes are found to be specific to strain 2. The blue line is the fit to the originally suggested exponential decay function [3].